Method of producing metallic bodies



y 22, 1952 B. w. GONSER ET AL 2,604,395

' METHOD OF PRODUCING METALLIC BODIES Filed Nov. 19, 1945 DE m N R MU OFC Fig. 1

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BRUCE W. GoNsER & EDWARD E. SLOWTER INVENTORS ATTQRNEY Patented July 22,1 952 UNITE" STAT i5;

TENT OFFICE METHGD 0F PRODUCING 'METALLIC BODIES Application November19, 1945, Serial No. 629,630

11 Claims.

This invention relates to the production of dense acid-resistant platesof tantalum or columbium upon a base metal to which the plating isbonded. By the process of thi invention it is possible to producearticles consisting of a base metal completely protected by an integralcoating of tantalum or columbium which renders the article im mune toattack by strong acid. By the process of this invention it is alsopossible to produce me" tallic tantalum or columbium.

It should be understood at this point that where the term tantalum isused, it refers also to columbium and. alloys of tantalum and columbium,ranging from all tantalum to all co lumbium, unless it be apparent'thatspecific reference is made. only to the element tantalum.

It is known that compounds of tantalum such as the halides, particularlythe chloride, are de composed at elevated temperatures in the presenceof hydrogen to produce more or less impure hered and formed a permanentprotective coating. The present, process .is animprovement on theheretofore known methods of halidereduction which results in thedeposition of. a mooth, dense,

acid-resistant and impervious plating of tantalum upon basemetals whichmay not .be acid-resistant.

As base. materials a ,wide variety of metals and alloys are suitable. Byway of example it may be mentioned that satisfactory results have beenobtained With: copper, copper plated metals, molybdenum, nickel-ironalloys, copper-nickel alloys,

, both those rich in copper. and those rich in nickel,

and various steels, particularly chrominum-nickel steels of thestainless type. By this invention tantalum may also be deposited as aplating upon a base of metallic tantalum. It will be obvious that themethod of our invention will not be applicable to metals or alloys whichmelt below the minimum temperature forrthe operation of our invention;which Will later be :shown .to be about In brief, this inventioncomprises volatilizing a suitable tantalum or columbium compound, forexample, a tantalum halide, and especially the chloride, in anatmosphereof purified hydrogen, conveying the tantalum halide-hydrogenmixture to the metal surface to be plated without prematurelydecomposing the halide, and then causing the halide to decompose'in suchmanner that the tantalum formed by the reaction bonds to the metalsurface and forms a dense adherent plating thereon. "l-here are a largenumber of factors affecting the production of a protective metal platingupon a base metal, and each of these factors must be heldwithincarefully restricted limits if satisfactory plating is to be assured. Inthe plating of a base metal with columbium it is obvious that acolumbium compound would be employed, and by the use of a mixture of atantalum compound and a colum bium compound a mixture of the two metalswill be plated on the base metal.

It has been found that the temperatures to which the halides maybesubjected before utilization in the plating procedure arequite limited.The common halides of tantalum and columbium have boiling points asfollows:

As long as the halide-hydrogen mixture is maintained at temperaturesabove the boiling point of the halide, any proportion of halide may beobtained in the vapor o far as quantity only is concerned. Below theboiling point an amount of halide proportionalto its vapor pressure atsuch lower temperatures may be carried by the hydrogen.

The upper temperature limitto which the hydrogen-halide mixture may besubjected before plating is quitetcritical. :It has been found that ifthese halides are heated above about 500 C. to about 600 C. prior to thedesired deposition, the tantalum or columium halide is decomposed withthe production of powdery tantalum or columbium andthecorrespondinghalogen acid. This powdery metal has no useful value as aprotective coating, and it has been found that the acid thus formed bypremature decomposition may attack the base metal which it is desired toprotect. Because of this fact it is necessary that in carrying out theprocess M this-invention the hydrogen-halide-mixture be maintained attemperatures below this decomposition point until the atmospherecontacts the surface which is to be plated. For best results, it isdesirable to release the halide at a temperature close to its boilingpoint and to prevent the hydrogen-halide mixture from reaching atemperature greatly in excess of this value until it contacts the basemetal upon which the plating is to .be deposited. In plating extendedsections of material with an acid-proof coating, the atmosphere flowmust be adjusted so as to secure this condition. This means that thetemperature of the body being plated cannot exceed certain limits, whichwill be set forth in more detail below, in order that this prematuredecomposition may be avoided.

Unlike many plating reactions, that involved in the deposition oftantalum and columbium is largely not a replacement reaction wherein onemetal is replaced by another but is a straight deposition reactionwherein the metal halide is decomposed by hydrogen. The first action onmany metal surfaces may be replacement, but the reduction reaction withhydrogen quickly becomes predominant. If the metal halide concentrationin the plating atmosphere is excessive, some of the metal halide passesthrough the system without decomposition and deposition of metal.Theoretically th reaction by which the major portion of the metal isdeposited may be represented by reference to the theoretical reactioninvolving tantalum chloride and hydrogen. This reaction is as follows:

We have found that, as long as the proper temperature conditions aremaintained, the ratio of hydrogen to halide in the plating atmospheremay vary over fairly wide limits. However, for the production ofstrongly adherent places of appreciably thickness over extensive surfaceareas, sufficient hydrogen should be present to combine with essentiallyall of the acid radical released by the decomposition of the metalhalide during the deposition reaction. Optimum results are produced onmost base metals when the inlet gas contains at least twice thetheoretical amount of hydrogen necessary to combine with the acidradical set free by the decomposition of the metal halide. The preferredratio, therefore, of hy- .drogen atoms to metal atoms in the inet gas isat least to 1. When the concentration of hydrogen in the atmosphere istoo low, thinner, more or less porous coatings may be obtained which aregenerally unsatisfactory for acid resistance.

Hydrogen concentrations in excess of 10 to 1 ratio set forth above maybe used with excellent results; however, too high a concentration ofhydrogen tends to decrease the speed with which the desired coating isproduced. The hydrogen chloride produced by the deposition exerts a backpressure on the decomposition reaction, of course, but it has been foundthat the maintenance of the gas at the 10 to 1 ratio given aboveproduces satisfactory results in most cases.

It is within the scope of this invention to noted before, tantalum andcolumbium halides appear to initiate spontaneous decomposition byhydrogen at about 500 C. to 600 C. However, the deposition produced bythis spontaneous decomposition tends to be loose, nonadherent andporous, these properties being undesirable in producing a protectiveplating. The platin atmosphere, therefore, should not be permitted toexceed this temperature until it contacts the base upon which thecoating is to be produced. The minimum temperature at which smooth, thincoatings are obtained depends, to a large extent, upon the particularbase metal being used. For example, very satisfactory coatings can bproduced on copper and molybdenum at a temperature of about 500 C., andthis temperature is preferred in the deposition of these metals onmolybdenum. A temperature of about 800 C. is preferred for depositingcoatings on iron; a temperature of about 1000 C. is preferred fornickel. Under proper conditions, temperatures as high as 1300 C. may beused for coatin most metals which, of course, have sufficiently highmelting points. Thus, coatings may be obtained over the general range offrom about 500 C. to about 1300 C.

At the higher temperatures in this range the alloying action between thedeposited tantalum or columbium and the base metal may become excessiveand produce a rough alloyed coating which does not possess the desiredacid-resistance. Even if alloying action is not rapid, the coating isapt to be rough and uneven and is so nonuniform that its performancecannot be predicted. Of more importance is the fact that when these hightemperatures are used at the surface being plated, the halide may bedecomposed before it reaches the surface, thereby preventing effectiveplating. Optimum plating temperatures for the practice of this inventionappear to be mainly in the range of about 500 C. to about 1150 C. withthe more rapid, plating taking place at th higher temperatures. However,some base metals cannot be heated to the higher temperatures withoutmelting, alloying excessively or undergoing undesirable structuralchanges. In these cases it is necessary to plate more slowly at thelower temperatures sinc the rate of deposition is dependent upon theplating temperatures and upon the hydrogen halide and the metal halidecontent of the gas above the surface being plated; in general, lowerplating temperatures favor more duetile deposits. The platingtemperature may be adjusted with respect to the gas composition tosecure a uniform coating over an extended surface. It will be obvious tothose skilled in the art, with the aid of the present specification, tochoose the appropriate ratios of hydrogen to halide and temperatures,depending upon the base metal which it is desired to coat or plate.

The hydrogen used for the plating reaction of this invention alsorequires careful control. The tantalum and columbium halides used in theplating reaction hydrolize very easily. Any oxygen or water vaporpresent in the hydrogen reacts With the halides to form oxy-compoundshalide, and the surface of the base metal should be suitably cleaned toeliminate all traces of oxides and scale. In fact, the presence ofdissolved oxygen in the base metal may, in some instances, prevent theformation of satisfactory coatings. Other reducing gases such as carbonmonoxide and methane are not satisfactory for this plating. Other gasessuch as nitrogen, carbon dioxide, or hydrocarbons, should be excludedfrom the plating atmosphere because of the ailinity of tantalum andcolumbium for these gases at elevated temperatures and the difficulty ofremoval of any gaseous element'from tantalum and columbium excepthydrogen.

In applying a protective coating of tantalum or columbium according tothis invention, it will be apparent that the base metal or alloy mustnot melt, soften to a great extent, or undergo undesirable changes instructure at the plating temperatures (500 C. or above). In addition,the tantalum or columbiuin must bond to the base metal so as to produceadherent platings. Copper, nickel, molybdenum, nickel-iron alloys,copper-nickel alloys and various plain carbon and alloy steels have beenfound to be suitable base metals for deposition of a tantalum andcolumbium plate. In plating various base metals, the base may beprovided with a suitable electrodeposited coating or layer of copperand-the tantalum or columbium deposited on the copper layer inaccordance with our invention. It'is believed that a very slightalloying action between the tantalum or columbium plate and the basemetal is desirable to secure the desiredbond, and this is offered as apossible explanation of the method by which bonding occurs, althoughthis is not intended to limit the invention. Nickel and high nickelalloys, such as Monel metal, are particularly good base materials, sincethe tantalum plate, as produced under the conditions of this invention,bonds to nickel in a very effective manner. Figure 2 shows the type ofbond obtained with nickel. Other metals produce a similar type of bond,although'it is apparent that'the bond strength may not be as high, ormay be highe depending'upon the base metal.

Having thus described the general features of the invention, aparticular example'will be explained'to illustrate the operation of theprocess. For the purpose of illustration, reference is made to Fig. 1 ofthe accompanyingdrawing in which the various refinements of theoperation have been eliminated and-only the basic essentials of theinvention shown. In this example theinvention is employed to platea'sectionof the inner wall of a metallic tube with tantalum, wherebythis section may be're'ndered acid-proof. As illustrated in the drawing,hydrogen from any "desirable source, for example, a tank, asillustrated, is passed first through a meter, thence through acombustion furnace which maydesirably' be furnished with catalyticpacking to reduce the temperature of reaction, thence through apreliminary drier containing, for example, calcium chloride, and thenceinto a final drierwhich is desirably filled with phosphorus pentoxide.The purified hydrogen then passes in succession through two furnaces,the'first for vaporizing the plating agent, for example, tantalumchloride, and the second in which the plating reaction is carried out.The effluent gas and vapor are desirably passed through a trap forcatching the unused tantalum chloride, and a condenser for recoveringthe hydrogen chloride. The resulting hydrogen is then available forrecycling in the system.

In operating the apparatus described above, the specimen to be plated isplaced in position in the plating furnace and the hydrogen turned on.

When the hydrogen has flowed through the apparatus for a suificientlength of time to provide a pure hydrogen atmosphere, the heating of theplating furnace is begun. The temperatureof the various portions of theheated section is adjusted with respect to the gas supply (of hydro-'-gen and tantalum halide) which is to be used so as to secure the desireduniformity of deposit. When the desired temperature conditions areobtained in the plating furnace, the vaporizing furnace is then heatedto a temperature at which the desired rate of tantalum halidevolatilization is obtained. This rate may be such with respect to theflow of hydrogen that the ratio of hydrogen atoms to tantalum atoms inthe entrance gas is about 10 to 1. When this mixture is passed over thesection to be plated, a metallic plate is formed on the base metal andis bonded thereto. The plating reaction is continued until the desiredthickness of plate is deposited; then when the halide supply is cut off,as for example, by ceasing to heat the vaporizing furnace, the platedarticle is allowed to cool in the purified atmosphere.

It appears that for reasonable thicknesses of plate the amount of platedeposited increases linearly with time. In all cases care must be takenthat the tantalum chloride is notheated above about 500 C. to 600 C.before contacting the surface to be plated in order to avoid spontaneousdeposition of the undesirable form of tantalum which slowly deposits inthis temperature range. The tube prepared by this process, upon removalfrom the apparatus, will have a dense, adherent, acid-resistant tantalumplating upon the section which has been treated. The plating produced bythis invention is smooth and impervious to attack by such reagents ashydrochloric acid and aqua regia at normal temperatures. Inasmuch astantalum cannot readily be electrodeposited to satisfy such severerequirements, the process disclosed permits the production of linedpipes and vessels and plated parts of intricate design which aresatisfactorily resistant to acid attack. Articles produced by thisplating process are less costly than articles of solid tantalum, yet areas satisfactory for many purposes. In the plating of many articles it isdesirable to heat the base metal by induction. In this manner the heatmay be concentrated in the article being plated and there is lesstendency forfthe plating atmosphere to decompose spontaneously prior tocontact with the metal surfaces and produce a porous deposit or to plateon the furnace walls.

While the coating produced by the method of this invention is adherentto the base metal, it is possible to plate a thick coating of tantalumor columbium upon a thin piece of base metal.

certain amount of hydrogen is taken up by the deposited metal. For manypurposes this does not interfere with the uses to which the platedarticle may be put. However, if it is desired to remove the hydrogen,the procedure disclosed in the patent to Austin, No. 2,015,509, may beemployed, for example.

Fig. 2 illustrates, at a magnification of about 500, the cross sectionof a tantalum plate upon a nickel base as produced according to ourinvention. The etchant used attacks the nickel particularly near thejunction with the tantalum alloy. .The' polishing scratches appearing inthe tantalum zone were left there deliberately in order to show thedifference in physical properties of the three zones. It appears thatthe initial portion of the tantalum deposited on the base forms an alloywith the base metal. Thereafter a substantially pure plate is laid down.In the case of the plate upon nickel, it appears that a series ofintermetallic compounds are formed, judging from the banded structurebetween the base metal and the tantalum plate.

It is to be understood that a columbian plate may be formed in the samemanner as the tantalum plate. If a tantalum-columbium plate is desired amixture of tantalum halide and a columbian halide may be employed; theratio of the halides being such as to yield the desired ratio of themetals.

It is to be further understood that the foregoing description is merelyillustrative of the invention and that various modifications willsuggest themselves to those skilled in the art, and may be made withoutdeparting from the spirit and scope of the invention.

We. claim: 7

1. The. method of depositing an integrally bonded, protective coating ona metal base having a melting point above about 500 C. whichcomprises'forming a mixture of hydrogen and the vapor of a volatilemetal halide selected from the group consisting of tantalum halides,columbium halides and mixtures thereof, the mixture of hydrogen andvolatilized metal halide being substantially freefrom carbon-containinggases, water vapor and oxygen, the amount of hydrogen present in saidmixture being sufficient to combine with essentially all of the acidradical released by the decomposition of the metal halide when the metalhalide is heated to a temperature above about-500 C., maintaining themixture of hydrogen and volatilized metal halide at a temperature abovethe volatilization temperature of the metal halide but below about 500C., heatin the metal base to a temperature between about 500C. and 1300C., and passing the said mixture of hydrogen and volatilized metalhalide into contact with the heated metal base.

2. The method of depositing an integrally and volatilized metal halideat a temperature above the volatilization temperature of the metalhalide and below about 500 C., heating the metal base to a temperaturebetween about 500C. and 1300 C. and passing the mixture of hydrogen andvolatilized metal halide into contact with the heated metal base toproduce a smooth, dense,

impervious and adherent plateof the metal on the metal base. 1

3. The method of depositing an integrally bonded, protective coating ona metal base having a melting point above about'500 C. whichcomprisesforming a mixture of hydrogen and a volatilized tantalumhalide, the mixture being substantially free of carbon containing gases,water vapor and oxygen, the atomic ratio of hydrogen to metal beingabout 10:1, maintaining the mixture at a temperature above thevolatilization temperature of the tantalum halide but below 500 C.,heating the metal base to a temperature between about 500 C. and 1300 C.and passing the mixture into contact with the heated metal base toproduce a smooth, dense, impervious and adherent plate of tantalum tnthe metal base.

4. The method of depositing an integrally bonded'protective coating on ametal base having a melting point above about 500 C. which comprisesforming a mixture of hydrogen and volatilized tantalum chloride, themixture being substantially free of carbon containing gases, water vaporand oxygen, the atomic ratio of hydrogen to tantalum being about 10:1,maintaining the mixture at a temperature above the volatilizationtemperature of tantalum chloride but below about 500 C., heating themetal base to a temperature between about 500 C. and 1300 C. and passingthe mixture into contact with the heated metal base to produce a smooth,dense, impervious and adherent plate of tantalum on the metal base.

5. The method of depositing an integrally bonded protective coating on amolybdenum surface which comprises forming a mixture of hydrogen andvolatilized tantalum chloride, the mixture being substantially free ofcarbon containing gases, water vapor and oxygen, the atomic ratio ofhydrogen to tantalum being about 10:1, maintaining the temperature ofthe mixture at a temperature above the volatilization temperature oftantalum chloride but below 500 C., heating the molybdenum surface to atemperature of at least about 500 C. and passing the mixture intocontact with the heated surface.

6. The method of depositing an integrally bonded protective coating on acopper surface which comprises forming a mixture of hydrogen and.volatilized tantalum chloride, the mixture being substantially free ofcarbon containing gases, watervapor and oxygen, the atomic ratio ofhydrogen to tantalum being about 10:1, maintaining the temperature ofthe mixture at a temperature above the volatilization temperature oftantalum chloride but below 500 C., heating the copper surface to atemperature of at least about 1000 C. and passing the mixture intocontact with the heated surface.

'7. The method of depositing an integrally bonded, protective coatingon'a nickel surface heated body to produce a smooth, dense, impervioneand adherent plate of tantalum on the nickel surface.

8. The method of producing columbium which comprises forming a mixtureof hydrogen and volatilized columbium halide, the mixture of hydrogenand columbium halide being substantially free of carbon containinggases, water vapor and oxygen, the atomic ratio of hydrogen to columbiumbeing about :1, maintaining the temperature of the mixture at atemperature above the volatilization temperature of the columbium halidebut below 500 C., passing the said heated mixture over a metal baseheated to a temperature between 500 C. and 1300 0., whereby thecolumbium halide is decomposed and columbium is deposited on the metalbase, and separating the deposited columbium from the metal base.

9. The method of producing a metallic body of the group consisting oftantalum, columbium and mixtures of tantalum and oolumbium whichcomprises providing a metal base having a melting point above about 500(3., forming a mixture of hydrogen and the vapor of a volatile metalhalide selected from the group consisting of tantalum halides, columbiumhalides and mixtures thereof, the mixture of hydrogen and volatilizedmetal halide being substantially free of carbon containing gases, watervapor and oxygen, the atomic ratio of hydrogen to metal being about10:1, maintaining the mixture of hydrogen and volatilized metal halideat a temperature above the volatilization temperature of the metalhalide but below about 500 C., heating the metal base to a temperaturebetween about 500 C. and 1300 C., passing the mixture of hydrogen andvolatilized metal halide into contact with the heated metal base toproduce a smooth, dense, impervious and adherent plate of the metal onthe metal base and separating the deposited plate from the metal base.

10. The method of producing a tantalum body which comprises providing ametal base having a melting point above about 500 C'., forming a mixtureof hydrogen and the vapor of a volatile tantalum halide, the mixture ofhydrogen and volatilized tantalum halide being substantially free ofcarbon containing gases, water vapor and oxygen, the atomic ratio ofhydrogen to tantalum being about 10:1, maintaining the mixture ofhydrogen and volatilized tantalum halide at a temperature above thevolatilization temperature of the tantalum halide but below about 500C'., heating the metal base to a temperature between about 500 C. and1300 C., passing the mixture of hydrogen and volatilized tantalum halideinto contact with the heated metal base to produce a smooth, dense,impervious and adherent tantalum plate on the metal base and separatingthe deposited tantalum from the metal base.

11. The method of producing a tantalum body which comprises providing ametal base having a melting point above about 500 C., forming a mixtureof hydrogen and the vapor of a volatile tantalum chloride, the mixtureof hydrogen and volatilized tantalum chloride being substantially freeof carbon containing gases, water vapor and oxygen, the atomic ratio ofhydrogen to tantalum being about 10:1, maintaining the mixture ofhydrogen and volatilized tantalum chloride at a temperature above thevolatilization temperature of the tantalum chloride but below about 5000., heating the metal base to a temperature between about 500 C. and1300 0., passing the mixture of hydrogen and volatilized tantalumchloride into contact with the heated metal base to produce a smooth,dense, impervious and adherent tantalum plate on the metal base andseparating the deposited tantalum from the metal base.

BRUCE W. GONSER. EDWARD E. SLOWTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 553,296 Aylsworth Jan. 21, 1896840,246 Parker et al. Jan. 1, 1907 1,019,394 Weintraub Mar. 5, 19121,149,701 Thowless Aug. 10, 1915 1,180,614 Simpson Apr. 25, 19161,497,417 Weber June 10, 1924 1,671,213 Van Arkel et al May 29, 19282,313,410 Walther Mar. 9, 1943 2,344,138 Drummond Mar. 14, 1944

9. THE METHOD OF PRODUCING A METALLIC BODY OF THE GROUP CONSISTING OFTANTALUM, COLUMBIUM AND MIXTURES OF TANTALUM AND COLUMBIUM WHICHCOMPRISES PROVIDING A METAL BASE HAVING A MELTING POINT ABOVE ABOUT 500*C., FORMING A MIXTURE OF HYDROGEN AND THE VAPOR OF A VOLATILE METALHALIDE SELECTED FROM THE GROUP CONSISTING OF TANTALUM HALIDES, COLUMBIUMHALIDES AND MIXTURES THEREOF, THE MIXTURE OF HYDROGEN AND VOLATILIZEDMETAL HALIDE BEING SUBSTANTIALLY FREE OF CARBON CONTAINING GASES, WATERVAPOR AND OXYGEN, THE ATOMIC RATIO OF HYDROGEN TO METAL BEING ABOUT10:1, MAINTAINING THE MIXTURE OF HYDROGEN AND VOLATILIZED METAL HALIDEAT A TEMPERATURE ABOVE THE VOLATILIZATION TEMPERATURE OF THE METALHALIDE BUT BELOW ABOUT 500* C., HEATING THE METAL BASE TO A TEMPERATUREBETWEEN ABOUT 500* C. AND 1300* C., PASSING THE MIXTURE OF HYDROGEN ANDVOLATILIZED METAL HALIDE INTO CONTACT WITH THE HEATED METAL BASE TOPRODUCE A SMOOTH, DENSE, IMPERVIOUS AND ADHERENT PLATE OF THE METAL ONTHE METAL BASE AND SEPARATING THE DEPOSITED PLATE FROM THE METAL BASE.